In known engine bearers or mountings of this kind, the lower member of the mounting, which is supported on the vehicle chassis, typically is either of a cup-shaped or a U-shaped configuration, depending on the space available for installation, while the upper member is in the form of a ball or wedge. A peripheral, annular shear spring member or at least two block-like shear spring members of rubber are arranged or vulcanised in position respectively between the lower member and the upper member. With an engine mounting of this kind, both high-frequency, low-amplitude oscillations or vibration, as will be produced by the engine when running normally, and also low-frequency, high-amplitude oscillations or vibration produced when the engine is starting up, when the engine is running at low speed, or due to the excitation effect of the roadway, are transmitted undamped from the upper member of the mounting into the shear spring member or members. The undamped low-frequency oscillations give rise to inadmissibly large movements.
Although it is known for a hydraulic shock absorber for damping the oscillations which occur, to be additionally provided between the engine and the vehicle chassis, a disadvantage is that, besides damping the low-frequency, high-amplitude oscillations which occur, the high-frequency oscillations are also damped, and this results in undesirable transmission of noise. Apart from the additional expense, it is necessary to provide a means for mounting the arrangement, and a particular form of mounting is necessary.
Single-chamber mountings with a hydraulic damping action are also known for supporting engines in passenger vehicles, such mountings producing severe damping in respect of low-frequency, high-amplitude oscillations. It would be theoretically possible for mountings designed in the above-indicated manner to be used in trucks, motor coaches or the like utility vehicles. However, the very high engine weight results in such high levels of loading on the mountings that the mountings would have to be of a size which is no longer acceptable but which in particular is no longer feasible from the structural design point of view.
The invention is therefore based on the problem of so designing an engine mounting for trucks, motor coaches or the like utility vehicles, without a high level of expenditure, so that it is also possible to damp the low-frequency, high-amplitude oscillations and to avoid damping, and the transmission of noise which results therefrom, in respect of high-frequency, low-amplitude oscillations.
To solve this problem, in an engine mounting as set forth at the beginning of this specification, the present invention proposes that a hydraulic-action springing and damping means is additionally arranged between the lower member and the upper member of the mounting. The additional hydraulic springing and damping means carries only a comparatively small proportion of the engine mounting load, but it provides effective damping in respect of low-frequency oscillations. The low level of engine mounting load makes it possible for the springing and damping means to be of a very small construction, similarly as in the case of passenger vehicles, and to be disposed in the engine mounting, preferably in the region of the upper member thereof.
The springing and damping means advantageously comprises a main body member which is supported on the lower member of the engine mounting and which is connected by way of a rubber spring to the upper member of the mounting, and a diaphragm which is clamped in the upper member of the mounting and which, in conjunction with the main body member and the rubber spring, defines a chamber which is filled with damping fluid. The chamber is in communication by way of a throttle aperture with an expansion or compensation chamber which is partially enclosed by a resilient folding bellows means and which receives without pressure a portion of the damping fluid from the fluid chamber. By virtue of this arrangement, it is possible to produce the springing and damping means, by using the upper member and the lower member of the engine mounting, that is to say, without a high level of additional expenditure.
In accordance with a preferred embodiment of the invention, the throttle aperture is disposed in the diaphragm, and the compensation or expansion chamber is provided at the side of the diaphragm which is remote from the fluid-filled chamber, and is defined by the diaphragm and the bellows means which is fitted in the upper member of the engine mounting. This has the advantage that the springing and damping means operates independently of the condition of spring stroke movement of the diaphragm, and any build-up of pressure in the chamber acts on the diaphragm on both sides.
Further details, features and advantages of the subject matter of the invention are described in greater detail hereinafter with reference to an embodiment shown in the accompanying drawing.